The present invention relates to an image processing technique that obtains an output image with reduced shake by performing coordinate transformation processing as shake correction processing to an image captured by an image-pickup apparatus.
Shake correction methods provided in image-pickup apparatuses include optical image stabilization and electronic image stabilization. The electronic image stabilization selects as a take-out area a region to be actually output (e.g., recorded or displayed) from within one frame image that is generated by use of an image-pickup device, and moves the take-out area in accordance with amount of shake for each frame. Then, coordinate transformation processing is applied to each take-out area image to thereby output an image with reduced shake (or a shake-corrected image).
Shake of an image-pickup apparatus can be detected by using an angular velocity sensor or angular acceleration sensor, or by comparing input images for two successive frames to detect motion vectors on the images as shake.
Shake appearing on an image includes combinations of various types of shake such as translation and rotation. Besides, characteristics of apparent shake on an image vary depending on the amount of shake or image-taking conditions such as zooming position of an imaging optical system. Accordingly, a technique is desired that provides properly shake-corrected images irrespective of various situations of shake occurrence.
For example, Japanese Patent Laid-Open No. 2002-116476 proposes a shake correction technique that uses an angular velocity sensor for shake detection. With this technique, although shake in the direction of panning and/or tilting (panning/tilting shake) can be detected, translational shake cannot be detected. Thus, in normal image-taking, shake correction is performed on the assumption that translational shake can be approximated to shake in the direction of panning or tilting, but in close-up image-taking, shake correction itself is not performed because the approximation does not hold in close-up image-taking.
Japanese Patent Laid-Open No. 2004-227003 proposes a shake correction technique that allows selection of an image shake correction characteristic appropriate for various image-taking conditions (i.e., a mode in which cut-off frequency for shake correction is high and a mode in which the cut-off frequency is low) and/or the range of shake correction (i.e., a range in which correction optical devices can move).
However, although the technique proposed in Japanese Patent Laid-Open No. 2002-116476 can provide a properly shake-corrected image except in close-up image-taking, it cannot provide a shake-corrected image in close-up image-taking because it does not perform shake correction itself in close-up image-taking. The shake correction technique proposed in Japanese Patent Laid-Open No. 2004-227003 is mainly focused on optical image stabilization and is not applicable to electronic image stabilization.